AdvertisementU.K. Lab Says It Doesn't Know Nerve Agent's 'Precise Source,' Drawing Russian RetortApril 03, 2018Colin DwyerfacebookEmailThe Defence Science and Technology Laboratory in Porton Down, U.K., seen last month. Researchers at the lab were tasked with testing the nerve agent used to poison Sergei Skripal and his daughter, Yulia, in early March. (Getty Images)